Data Layer: Dynamic Styling

This example uses a data layer to dynamically change the appearance of some KML feature objects when the user hovers over or clicks them.

Read the documentation.

var map;
function initMap() {
  map = new google.maps.Map(document.getElementById('map'), {
    zoom: 4,
    center: {lat: -28, lng: 137}
  });

  // Load GeoJSON.
  map.data.loadGeoJson(
      'https://storage.googleapis.com/mapsdevsite/json/google.json');

  // Color each letter gray. Change the color when the isColorful property
  // is set to true.
  map.data.setStyle(function(feature) {
    var color = 'gray';
    if (feature.getProperty('isColorful')) {
      color = feature.getProperty('color');
    }
    return /** @type {!google.maps.Data.StyleOptions} */({
      fillColor: color,
      strokeColor: color,
      strokeWeight: 2
    });
  });

  // When the user clicks, set 'isColorful', changing the color of the letters.
  map.data.addListener('click', function(event) {
    event.feature.setProperty('isColorful', true);
  });

  // When the user hovers, tempt them to click by outlining the letters.
  // Call revertStyle() to remove all overrides. This will use the style rules
  // defined in the function passed to setStyle()
  map.data.addListener('mouseover', function(event) {
    map.data.revertStyle();
    map.data.overrideStyle(event.feature, {strokeWeight: 8});
  });

  map.data.addListener('mouseout', function(event) {
    map.data.revertStyle();
  });
}
<div id="map"></div>
/* Always set the map height explicitly to define the size of the div
 * element that contains the map. */
#map {
  height: 100%;
}
/* Optional: Makes the sample page fill the window. */
html, body {
  height: 100%;
  margin: 0;
  padding: 0;
}
<!-- Replace the value of the key parameter with your own API key. -->
<script async defer
src="https://maps.googleapis.com/maps/api/js?key=AIzaSyCkUOdZ5y7hMm0yrcCQoCvLwzdM6M8s5qk&callback=initMap">
</script>

Try it yourself

You can experiment with this code in JSFiddle by clicking the <> icon in the top-right corner of the code window.

<!DOCTYPE html>
<html>
  <head>
    <title>Data Layer: Dynamic Styling</title>
    <meta name="viewport" content="initial-scale=1.0">
    <meta charset="utf-8">
    <style>
      /* Always set the map height explicitly to define the size of the div
       * element that contains the map. */
      #map {
        height: 100%;
      }
      /* Optional: Makes the sample page fill the window. */
      html, body {
        height: 100%;
        margin: 0;
        padding: 0;
      }
    </style>
  </head>
  <body>
    <div id="map"></div>
    <script>

      var map;
      function initMap() {
        map = new google.maps.Map(document.getElementById('map'), {
          zoom: 4,
          center: {lat: -28, lng: 137}
        });

        // Load GeoJSON.
        map.data.loadGeoJson(
            'https://storage.googleapis.com/mapsdevsite/json/google.json');

        // Color each letter gray. Change the color when the isColorful property
        // is set to true.
        map.data.setStyle(function(feature) {
          var color = 'gray';
          if (feature.getProperty('isColorful')) {
            color = feature.getProperty('color');
          }
          return /** @type {!google.maps.Data.StyleOptions} */({
            fillColor: color,
            strokeColor: color,
            strokeWeight: 2
          });
        });

        // When the user clicks, set 'isColorful', changing the color of the letters.
        map.data.addListener('click', function(event) {
          event.feature.setProperty('isColorful', true);
        });

        // When the user hovers, tempt them to click by outlining the letters.
        // Call revertStyle() to remove all overrides. This will use the style rules
        // defined in the function passed to setStyle()
        map.data.addListener('mouseover', function(event) {
          map.data.revertStyle();
          map.data.overrideStyle(event.feature, {strokeWeight: 8});
        });

        map.data.addListener('mouseout', function(event) {
          map.data.revertStyle();
        });
      }
    </script>
    <script async defer
    src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&callback=initMap">
    </script>
  </body>
</html>